The present invention relates to an apparatus for determining the internal outline of a duct or cavity and, in particular, to an apparatus for determining the internal impression of the auditory canal.
It is known that modern internal hearing prostheses have to fit the shape of the user's auditory canal as well as possible. For this purpose, it is necessary to have an accurate copy of the internal impression of the auditory canal. According to conventional techniques, this is achieved by introducing quick-setting mouldable material into the auditory canal. Once the material has set, it is removed from the ear, thus providing a cast of the canal. Finally, the surface of the cast is subjected to a scanning process and is mapped so as to produce data that can be stored by a computer.
For example, U.S. Pat. No. 5,487,012 describes a method for the scanning of a cast of an auditory canal in order to obtain a digital image which is then processed in order to design the hearing prosthesis.
These conventional techniques for determining the internal profile of the auditory canal have some disadvantages, amongst which is their inevitable invasive nature and the complexity and number of steps that are necessary to produce a cast suitable for the manufacture of a mould for the preparation of the outer shell of the hearing prosthesis, since the cast extracted from the ear has to be processed further in order to eliminate its imperfections.
The document WO 02/091920 describes an apparatus for obtaining geometrical data relating to the internal surface of the ear, comprising a probe with a rod portion containing at least one light guide and a light source at the proximal end of the light guide. The apparatus further comprises a distal portion which can be inserted in the ear canal and has means for directing the light onto at least one point of the internal surface of the ear canal. For this purpose, the above-mentioned means comprise a mirror with a conical surface. A probe of this type is quite bulky and inefficient, particularly when the ear canal is tortuous.